The present invention relates to optical multi/demultiplexers, particularly those for use with optical fibers.
In optical communications systems there is a need for multiplexing different wavelength signals from a plurality of optical fibers into a single fiber and vice versa. Among the important considerations for a device performing such a function is its complexity, its insertion loss, and its cross talk.
One type of optical fiber multi/demultiplexer device is described in the U.S. Pat. No. 4,111,524 issued Sept. 5, 1978, to Tomlinson. In this device a GRIN (graded refractive index)-rod lens collimates different wavelength light signals from signal source fibers on one face to its other face. A reflective diffraction grating is spaced from the other face at such an angle that the different wavelength components of the source signals are differentially reflected back into the GRIN-rod to emerge at the first face at an output location, where they now pass in multiplexed form into a single receptor fiber. The nature of this arrangement, however, is such that the fiber geometry itself limits the channel spacing and bandwidth.
Other multi/demultiplexer devices which have been described involve multilayer dielectric interference filters in conjunction with lenses in various configurations, such as for example the structure described in "Low-Loss Optical Multi/demultiplexer Using Interference Filters," Optical Communication Conference, Amsterdam, Sept. 17-19, 1979, pp. 11.5-1-11.5-3. These devices, however, are more complex and bulky than the above reflective grating device.